This invention relates to a power-supply unit particularly for direct-current motors of dual-current railroad locomotives using semiconductor equipment for speed control.
It is known that there are power-supply units using a 1,500 or 3,000-volt D-C source or a single-phase A-C source, particularly 25 or 50 kilovolts at 50 Hz or 60 Hz, for modern locomotives. The semiconductor equipment of such units, of the static type, comprises single-way bridge rectifiers divided into two fundamental categories for single-phase operation: fully controlled bridges or full thyristor bridges and semi-controlled bridges or mixed bridges; and drive choppers for a D-C operation.
It is also known that there is a power unit for supplying D-C current and A-C current to at least one traction motor, the electric circuit of which permits the re-use, in single phase, of the main semiconductor components, such as thyristors, of the chopper in order to provide a mixed bridge.
However, the electric circuit of such a unit has the disadvantage of using a great number of contactor components to modify the configuration of the unit from the chopper mode to the rectifier mode or vice-versa. Furthermore, this known unit does not permit regenerative braking in either A-C or D-C and it also has a poor power factor.